JPS6173920A - Stabilizing device for quantity of laser exposure - Google Patents

Abstract

PURPOSE:To stabilize the quantity of image recording exposure with good responsiveness by diffracting spectrally and comparing the output of an optical modulator for image modulation with a reference value, and feeding the difference signal back to an optical modulator for stabilizing the quantity of laser light. CONSTITUTION:A laser beam from a laser light source 1 is passed through the optical modulator 2a which stabilizes the quantity of the light and a polarizing plate 4a which limits the direction of its plane of polarization so that the transmittivity and reflectivity of a beam splitter 5a are constant, and diffracted spectrally by the splitter 5a, and the transmitted light is further passed through the optical modulator 2b for image modulation, polarizing plat 4b, beam splitter 5b, etc., to obtain image exposure light. The deviation from the reference value which is obtained by the spectral diffraction of the splitter 5b and a differential amplifier 14 is supplied to a differential amplifier 19 supplied with spectral light from the splitter 5b to perform feedback control over the modulator 2a, and diffraction efficiency variation due to the temperature drift of the modulator 2b is compensated with good responsiveness without performing feedback control over the modulator 2b directly. Consequently, the quantity of image recording laser exposure is stabilized with good responsibility.

Description

Detailed Description of the Invention (Field of Application in Industry A) The present invention relates to Ml that stabilizes the exposure m of a laser beam used for image scanning and recording, and in particular modulates the laser beam with the luminous intensity g41M to stabilize the image. Laser exposure m stabilization used in scanning recording systems 1iiff
It is related to.

(Prior Art) Normally, the intensity of the output light of a laser light source varies over time. Therefore, in order to obtain a laser light output with stable intensity, various devices have been proposed to remove this noise component outside the light source, and the present applicant has already proposed a device for removing this noise component outside the light source.
No. 917 proposes this type of device.

The above device is an acousto-optic modulator (AO) for stabilizing the amount of laser light.
M) is provided separately from the image modulation AOM, and this stabilizing AO
The amount of laser light is detected before or after the M, and a correction signal corresponding to the difference between this detected value and the reference value is sent to this stabilizing AOM.
The purpose is to stabilize the mountain by returning it to Mt.

However, although this device is capable of stabilizing the laser beam m from the light source, the diffraction efficiency fluctuates due to the humidity drift of the image modulation AOM, making it difficult to adjust the final output laser beam amount to a predetermined amount. It is difficult to set the value. Furthermore, since the plane of polarization of the beam rotates due to this temperature change, there is a problem in that the amount of laser light that is finally output varies in an optical system in which an optical member such as a beam splitter is placed after the image modulation AOM. There is.

As an example of a device that can eliminate the adverse effects caused by fluctuations in diffraction efficiency due to temperature drift of the AOM, there is the following conventional technology. That is, the modulated light obtained by adjusting the intensity with the AOM according to the image signal is separated by a beam splitter, the amount of light of the separated beam is detected by a photodetector, and the detected signal and image are detected. The difference signal obtained by this comparison is fed back to the AOM. According to this device, it is possible to stabilize the amount of laser light from the light source and to compensate for fluctuations in diffraction efficiency due to the 4-degree drift of the AoM. No consideration is given to zero-transfer development of the polarization plane due to drift. Therefore, since the beam reflectance and transmittance in the beam splitter change and the detection signal no longer corresponds to the amount of modulated light, the feedback performed for compensation ends up amplifying the light mvl. was there.

Furthermore, in the above-described apparatus in which the detection signal is fed back to the AOM for a-contact image modulation, good results have not been obtained in terms of responsiveness and extinction ratio.

(Object of the Invention) The present invention has been made in view of the above-mentioned problems, and it externally stabilizes the amount of laser light from a light source, and also eliminates fluctuations in diffraction efficiency and polarization caused by temperature drift of an AOM for image modulation. It is an object of the present invention to provide a highly responsive laser exposure stabilization device capable of compensating for surface rotation and stabilizing the image recording exposure amount.

(Structure of the Invention) The laser exposure m stabilization device of the present invention includes a light modulator 1 for stabilizing the amount of laser light, a light modulator for image modulation, and a light modulator for image modulation, l! A light plate and a beam splitter are placed on the optical path, and the beam splitter splits the output light from the light modulator for image modulation that has passed through the polarizing plate, detects the light intensity of the split beam, and uses this detection signal as a reference. This is characterized in that a difference signal obtained by comparing the signals is fed back to an optical modulator for stabilizing the amount of laser light.

<Effects of the Invention> The laser exposure m stabilization device of the present invention detects the output light from the image modulation light modulator and provides feedback for stabilizing the light amount. It is possible to compensate for fluctuations in diffraction efficiency due to temperature drift of the device, and the polarization plane of the beam is always set in a constant direction by a polarizing plate inserted between the optical modulator and the beam splitter, and then this beam is It illuminates the splitter so that its reflectance and transmittance are constant.
The reflected light or transmitted light from this beam splitter is
11glIm to stabilize the light quantity, it is possible to compensate for rotation of the beam polarization plane caused by temperature drift of the optical modulator.

Further, in this device, a control signal obtained based on the detection of the output light from the image modulation optical modulator is fed back to the optical modulator for stabilizing the laser beam M. Therefore, the present device can obtain extremely superior values in terms of responsiveness and extinction ratio compared to conventional devices that provide direct feedback to the optical modulator for image modulation.

(Actual arm) Hereinafter, embodiments of the laser exposure amount stabilizing device according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing one embodiment of a laser exposure amount stabilizing device according to the present invention.

Laser light source 1 that generates laser light IL and image scanning 1il
An acousto-optic sensor is placed in the optical path of the laser beam IL between l&! l
An iPJ (AOM) 2a is installed. light modulation a2a
is an acoustic wave device that diffracts the laser beam IL in accordance with the R11 pressure from the drive circuit Ha and separates the undiffracted light (zero-order light) Io from the diffracted light 11.

Diffraction light 1+ of the first order or higher is blocked by the light shielding plate 3a,
Only the 0th-order light 1G enters the polarizing plate 4a, and the 0th-order light ■' always has a polarization plane in a constant direction. is incident on the beam splitter 5a. The back part of the O-order light 1'o is guided to the photodetector 6a as reflected light IR, and transmitted light IT (IT-1'o I
m) is incident on the image modulation AOM 2b. 0th order light I
Since to always has a plane of polarization in a fixed direction, the intensity of the reflected light [R and the transmitted light 1T separated by the beam splitter 5a is proportional to the intensity of the zero-order light ['o].

The photodetector 6a is a photoelectric conversion element that outputs an electric signal according to the intensity of the received reflected light It, and its output signal is inputted to one terminal 9a of the differential amplifier 9. Differential amplifier 9
The reference signal 8 is input to the other terminal 9 of the . This differential amplifier 9 connects the output signal 8 from the photoelectric conversion element to the reference signal 8.
This is a four-way arithmetic operation that outputs an amplified difference signal 10 between the two and the same to the drive circuit Ha.

Picture full change mllll AOM2b ha AOM2a to l1i
It is a vlSll device which separates transmitted light IT into 0th-order light I2, 1st-order light 3, and higher-order diffracted light in response to a drive signal based on an image signal 12 from drive circuit +lb.

The O-order light I2 and the diffracted light of the second-order or higher order are blocked by the light shielding plate 3b, and only the first-order light I3 enters the polarizing plate 4b.

The polarizing plate 4b converts the primary light I3 into the primary light I's which always has a polarization plane in a fixed direction. The primary light I'3 enters the beam splitter 5b, and a part of it becomes the reflected light BR.
The transmitted light 1'T (1'T
-I'3 I'm) is irradiated onto the exposure section 15 of the image scanning device 16 as an exposure beam. Primary light 1'3
Since the light always has a plane of polarization in a fixed direction, the intensity of the reflected light 1'R and the transmitted light 1't separated by the beam splitter 5b is proportional to the intensity of the primary light I's.

The photodetector 6b is a photoelectric conversion element that outputs an electrical signal according to the intensity of the received reflected light 1'++, and its output 13
is input to one terminal 14a of the differential amplifier 14 and compared with the image signal 12 input to the other terminal 14b. The difference signal obtained through the comparison is input as the reference signal 8 to the terminal 9b of the differential amplifier 9.

In this actual FM mode, the beam light intensity from the light source 1 is stabilized by the first feedback control system formed by 2a - 5a - 9 - 11a - 2a, and the temperature drift of AOM 2b, more precisely, AOM 2b 2a compensates for fluctuations in diffraction efficiency and rotation of the beam polarization plane caused by temperature drift of the optical modulation element arranged in the
-2b -4b -5b -6b -14-9-Ha
This is done by a second feedback control system formed by -2a.

The polarizing plates 4a and 4b inserted in the two feedback control systems described above have the following important roles. If these polarizing plates 4a and 4b are not inserted, when the beam polarization plane is rotated due to temperature drift of the AOMs 2a and 2b, the beam split will change, and the beam I'0. It becomes impossible to accurately detect the intensity of I'3, and therefore control becomes impossible. In order to avoid this situation, Mr. Honjitsu 11MB installed a ring plate 4a, next to AOM 28°2b.
4b is inserted to adjust the beam reflectance. Also, in this embodiment, the second
In the feedback control system, control 1ffi is controlled by AOM.
Instead of feeding back to AOM 2b, it feeds back to AOM 2a. This is because if feedback is provided to the AOM 2b, problems such as poor responsiveness and an inability to obtain a large extinction ratio occur.

Note that the reason why the 0th-order light 1° of the output light from the AOM 2a is used is to increase optical efficiency, and the first-order light may also be used. Furthermore, the reason for using the primary light (3) of the output light from AOM2b is to widen the dynamic range.Modulation using an image signal, which requires a particularly wide range, requires the use of the primary light. This is because it is suitable. Of course, instead of primary light I3, O
It is also possible to use the second light (2).

FIG. 2 is a block diagram showing another actual IN aspect of the present invention. In the figure, parts that are the same as those in the embodiment shown in FIG. 1 are given the same reference numerals, and description thereof will be omitted.

This embodiment focuses on the fact that the temperature drift of 80M is very slow and that it is not necessary to constantly compensate for fluctuations in diffraction efficiency and rotation of the beam polarization plane caused by this temperature drift. A for image modulation using the blanking period of image scanning that does not require signal modulation.
A standard signal is input to the OM, and feedback control is performed periodically.

A reference signal 21 of a constant level is input to the terminal 14b of the difference #J amplification rj14, and the difference signal obtained by comparison is the sample hold signal 22 synchronized with the blanking period of image scanning. The input signal is sampled and held by the sample and hold circuit 23, and the difference signal continues to be sent to the terminals of the differential amplifier 9, overcoming the reference signal, until a new signal is held. The sample hold signal 22 is generated by a clock signal of a rotary encoder provided on the exposure drum of the image scanning device 216, and is generated in synchronization with the blanking period of image scanning.

On the other hand, an image signal 12 is inputted to the drive path 11b via an analog switch 24 during a period when the image is scanned on the exposure section 15, and is the same as the sample hold signal 22. The analog switch 24 is switched by this signal, and a standard signal (usually a signal at a constant level) is input.

According to the actual 111 aspect, in the actual IM aspect shown in FIG. However, such problems no longer occur, and there is no influence on the image signal during the image scanning period, and there is no problem in the image light modulation operation in the AOM.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the laser exposure totally stable upper limit according to the present invention, and FIG. 2 is a block diagram showing another actual IMR mode of the present invention.

Claims (1)

[Scope of Claims] A first light modulating means for modulating the laser light output from the laser light source, a first beam separating means for separating the modulated laser light into a reflected beam and a transmitted beam, the reflected beam and the transmitted beam. a first photoelectric conversion means that receives one of the transmitted beams and generates a first electrical signal according to the amount of the received beam; and compares the first electrical signal with a first reference signal. a feedback control circuit that generates a second electrical signal according to the difference between these two signals and controls the degree of modulation of the first optical modulation means based on the second electrical signal; a second light modulator that modulates the other beam according to a modulation degree based on a desired image signal and outputs it as a scanning exposure beam; and a second separation unit that separates the exposure beam into a reflected beam and a transmitted beam. means; second photoelectric conversion means for receiving one of these beams and generating a third electrical signal according to the amount of light of the received beam; a signal generating means provided to compare and generate the first reference signal according to the difference between these two signals; a signal generating means provided between the first light modulating means and the first beam separating means; A laser exposure amount stabilizing device comprising a polarizing plate provided between the second light modulating means and the second beam separating means.